Ultra hard iron-cobalt-molybdenum-nickel alloys

ABSTRACT

FERROUS BASE ALLOYS CONTAINING COBALT, MOLYBDENUM AND NICKEL IN CORRELATED AMOUNTS AFFORD EXCEPTIONALLY HIGH LEVELS OF HARDNESS, I.E., UP TO ABOUT ROCKWELL C (RC) 70. THE PRESENCE OF OTHER CONSTITUENTS IN CONTROLLED AMOUNTS, NOTABLY TITANIUM AND/OR ALUMINUM, IS BENEFICIAL.

March 6, 1973 c G B|EBER ET AL 3,719,474

ULTRA HARD IRON-COBALT-MOLYBDENUM-NTCKEL ALLOYS Original Filed Sept. 7,1966 Chsquz United States Patent M 3,719,474 ULTRA HARDIRON-COBALT-MOLYBDENUM- NICKEL ALLOYS Clarence George Bieber, Sulfern,N.Y., and John Raymond Mihalisin, North Caldwell, N.J., assignors to TheInternational Nickel Company, Inc., New York, N.Y. Original applicationSept. 7, 1966, Ser. No. 577,683, new Patent No. 3,485,620, dated Dec.23, 1969. Divided and this application Nov. 6, 1969, Ser. No. 874,142Int. Cl. C22c 39/00, 37/00 U.S. Cl. 75-123 8 Claims ABSTRACT OF THEDISCLOSURE Ferrous base alloys containing cobalt, molybdenum and nickelin correlated amounts afford exceptionally high levels of hardness,i.e., up to about Rockwell C (R 70. The presence of other constituentsin controlled amounts, notably titanium and/ or aluminum, is beneficial.

The present application is a divisional of our co-pending U.S.application Ser. No. 577,683 filed Sept. 7, 1966, now U.S. Pat.3,485,620.

The present invention relates to ferrous alloys and more particularly tonovel, martensitic ferrous alloys capable of affording exceptionallyhigh levels of hardness, to wit, up to about Rockwell C (R,,) 70..

As is generally known to those skilled in the art, research efforts havebeen somewhat intensified in recent years with the objective ofdeveloping alloys characterized by an extraordinarily high order ofhardness. This has been brought about, at least in part, as a result ofthe fact that operating conditions, e.g., temperatures, pressures, etc.,have become increasingly more severe in many areas of commercialactivity. In turn, this has focused attention on the need for articlesof manufacture capable of exhibiting outstanding resistance to wear andabrasion, properties which are a reflection of hardness. Among sucharticles might be noted dies, including cold drawing dies, bearings,axles, mandrels for drawing tubes, tools, races, etc.

In ferrous metallurgy, alloys in use for purposes contemplated hereinusually contain such elements as chromium, cobalt, molybdenum, vanadium,tungsten and substantial amounts of carbon. As high carbon alloys, theyare normally quenched, quenching being a prerequisite to achievingmaximum hardness. But by the same token, it is this aspect which cangive rise to the well known problems associated with distortion. Thesedrawbacks are rather well documented and it will suflice to but mentionthat measures must be taken to obviate the same. Further, many suchprior art alloys manifest an appreciable loss in hardness at moderatelyhigh temperatures, it being not uncommon to find alloys characterized bysubstantial hardness at room temperature but which upon exposure forrelatively short periods to elevated temperature undergo a significantloss of hardness. While satisfactory for certain applications, suchalloys would not be deemed suitable for relatively high temperatureapplications 0 the order of, say, about 1200 F.

It has now been discovered that hardnesses of about R 65 to 70 can beachieved with martensitic alloys containing special and correlatedamounts of certain constituents, notably iron, cobalt, molybdenum,nickel, carbon, aluminum and titanium.

It is an object of the present invention to provide novel, martensiticferrous alloys which are ultra hard, i.e., characterized by hardnessesof about R 65 and higher.

It is a further object of the invention to provide new and improvedferrous alloys characterized by a hardness 3,719,474 Patented Mar; 6,1973 upwards of about R 65, the hardness level being achieved by simpleheat treatment and without recourse to quenchmg.

Another object of the invention is to provide ultra hard ferrous alloyswhich greatly resist softening at temperatures as high as 1200 F.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in whichthere is depicted a chart in respect of cobalt and molybdenum contentspertaining to alloys within the invention as herein more fullydescribed.

Generally speaking and in accordance with the present invention, alloyscontemplated herein contain (in weight percent) from 10% to 40% cobalt;from 10% to 20% molybdenum, the cobalt and molybdenum being correlatedto represent a point within the area ACDFGHA of the accompanyingdrawing; nickel in an amount up to 5%, e.g., 1% to 5%; up to 2%, e.g.,up to 1%, carbon; up to 1.5%, e.g., up to 1%, titanium; up to 1.5%,e.g., up to 1%, aluminum, the sum of the titanium plus aluminum notexceeding about 1.5%; up to 0.5% manganese; up to 0.5% silicon; and thebalance essentially iron. As will be understood by those skilled in theart, the term balance or balance essentially used in referring to theiron content of the alloys does not exclude the presence of otherelements commonly present as incidental elements, e.g., deoxidizing andcleansing elements, and impurities ordinarily associated therewith insmall amounts which do not adversely affect the basic characteristics ofthe alloys. However, elements such as sulfur, phosphorus, hydrogen,oxygen, nitrogen and the like should be maintained at low levelsconsistent with good commercial practice.

Supplementary elements can be present in the alloys as set forth inTable I.

The total of supplementary elements should not exceed 10%,advantageously being not more than 7%. Tungsten can be used to replacemolybdenum in part on an equal atomic basis, i.e., two parts tungstenfor one part molybdenum, up to 10% tungsten by weight. However, thealloys are more difiicultly workable with tungsten and it is accordinglypreferable that tungsten not exceed 6%.

In carrying the present invention into practice care .must be exercisedwith regard to the respective amounts of the constituents in order thatthe alloys be of a martensitic structure (as distinct from a ferritic oraustenitic) and that this structure must be attained before aging;otherwise, full hardness will not be realized. Upon solidification of amelt the alloys are austenitic but the chemistry thereof is balancedsuch that the alloys transform to martensite upon cooling to, say, roomtemperature or lower. In relation to each other, excessive amounts ofone or more of the primary hardening elements molybdenum and cobalt, orthe toughening (brittle resistant) constituent nickel promotes theformation of retained austenite (austenite of such stability that itdoes not undergo transformation) and consequent loss in hardness. On theother hand, an insufiicient amount of one or more of these constituentscan lead to steels of the ferritic type as contemplated herein. It ismost advantageous in achieving highly satisfactory results that thealloys contain about 15% to 40% cobalt, about 12% to 18% molybdenum andabout 2% to 5% nickel with the cobalt and molybdenum being correlated torepresent a point falling within the area LBEJ KL of the accompanyingdrawing.

Carbon, while it can be present in the alloys up to 2%, is not at allessential. Where ductility and toughness are especially desired, itshould not exceed 0.05% and advantageously should not exceed about5.03%. But where the presence of carbides would be necessary for aparticular application, or otherwise useful, then, of course, highercarbon contents can be employed, e.g., up to 1%. For the purpose ofdeoxidation, malleabilization and the like, titanium and/or aluminum arebeneficial and the presence of one or both of these elements in anamount of about 0.1% to 0.5% each is beneficial. Also, in amounts ofabout 0.5% to 1.5% these constituents can confer enhanced hardness,particularly where the amounts of cobalt and molybdenum are on the lowside; however, the total amount of titanium and aluminum generally neednot exceed about 1%.

In processing the alloys, air or vacuum melting practice can beutilized, preferably followed by consumable electrode melting foroptimum effects. It is preferred to employ materials of high purity tothereby minimize the occurrence of inclusions, contaminants, etc.Initially formed cast ingots should be thoroughly homogenized as, forexample, by soaking, at a temperature of about 2200 F. to about 2300 F.for about one hour per inch of cross section. Thereafter, the alloys canbe hot worked (as by forging, pressing, rolling, etc.) and, if desired,cold worked to desired shape. A plurality of heating and hot workingoperations can be used and are advantageous to assure thoroughhomogenization of the cast structure through diffusion and to break upthe cast structure. Hot working can be satisfactorily carried out over atemperature range of 2300 F. or 2200 F. down to 1400 F., e.g., 2150 F.to 1500 F., with suitable finishing temperatures being about 2000" F.down to about 1500 F. Cooling from hot working is preferablyaccomplished by air cooling although furnace cooling, quenching, etc.,can be employed.

Subsequent to cooling from the hot working temperature to effect atransformation to the martensitic condition, the steels can be directlyaged by heating at a temperature of about 850 F. to 1000 F. for about100 hours to 0.1 hour, the longer aging periods being used inconjunction with the lower temperatures. Aging at 900 F. to 950 F. forabout 1 to 8 hours issatisfacto'ry. Where deemed advisable, a coldtreatment, e.g., as by refrigeration or cold working or both, can beused prior to aging. Such a treatment is of benefit in assuring themaximum conversion of austenite to martensite. Further, where deemednecessary, the steels can be subjected to a solution annealing treatmentover the range of about 1500 F. to about 2200 F. prior to aging;however, the temperature employed is dependent upon the molybdenumcontent such that the higher temperatures should beused with alloyscontaining molybdenum on the high' side of the molybdenum range. v

For the purpose of giving those skilled in the art a betterunderstanding of the invention, the following description and data aregiven:

Several alloys, the compositions of which are given in Table II (Alloys1 to 4 being within the invention and Alloys A through H being outsidethe scope thereof), were prepared either by air or vacuum melting. Uponsolidification ingots were soaked at 2200 F. to 2300 F. and thereafterhot worked (except Alloys B through H which were tested as small castspecimens). The alloys were then subjected to one or more of severaldifferent aging treatments given below (in many instances an agingtreatment was followed by a higher temperature treatment mainly for thepurpose of obtaining relative data as to the ability of the alloys toresist softening) I-Aged at 900 F. for 4 hours II-Aged at 900 F. for 8hours IIIAged at 925 F.950 F. for 1 hour. IV-Aged at 1000 F. for 1 hourVAged at 1150 F. for 1 hour VIAged or heated at 1200 F. for 4 hoursVIIAged or heated at 1200 F. for 8 hours VIII-Aged or heated at 1300 F.for 1 hour IX-Aged or heated at 1300 F. for 4 hours TABLE II Co, Mo, Ni,Ti, Al, Heat Hardperperperperpertreatness, Alloy cent cent cent centcent ment R 1 Alloys E through H were solution treated at 2,100 F. for 4home before aging. All alloys contained less than 0.05% carbon; Alloys 0and. D contained 10% and 20% tungsten, respectively.

From the data in Table II, it is clear that alloys within the inventionall manifested a satisfactory level of hardness. In addition, Alloys 1through 3 reflected the capability of resisting softening at relativelyhigh temperatures, e.g., 1200 F. In this connection, it is beneficialthat the alloys contain not more than about 4% nickel. In contrast toAlloys 1 to 4, Alloys A to C and E to H all exhibited inferior hardness.Alloy D achieved a satisfactory hardness level but only upon aging at anexcessively high temperature, to wit, 1200 F. Alloys which age in theregion of 1200" F. to hardness levels contemplated herein have aferritic base and are usually brittle. A further quite satisfactoryalloy range in accordance herewith is as follows: about 18% to 35%cobalt, about 14% to 18% molybdenum, the cobalt and molybdenum beingcorrelated to represent a point falling within the area ACDFGI-IA of theaccompanying drawing, about 1% to 4% nickel, up to 4% tungsten, up to0.05% carbon, 0.1% to 0.5% titanium, 0.1% to 0.5% aluminum, up to 0.25%manganese, up to 0.25 silicon, and the balance essentially iron.

In addition to dies, bearings, axles, mandrels and races, the presentinvention is useful in the production of tools such as high speeddrills.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. An alloy characterized by a hardness of about R 65 or higher whenaged within the temperature range of 850 F. to 1000 F., said alloyconsisting essentially of from 10% to 40% cobalt, from 10% to 20%molybdenum, the molybdenum and cobalt being correlated to represent apoint within the area ACDFGHA of the accompanying drawing, nickelpresent in an amount up to up to 0.05% carbon, up to 1.5% titanium, upto 1.5 aluminum, the sum of the titanium plus aluminum not exceedingabout 1.5%, up to 0.5% manganese, up to 0.5% silicon, up to tungsten, upto 2% columbium, up to 4% tantalum, up to 0.1% boron, up to 0.25%zirconium, up to 2% vanadium, up to 1% beryllium, up to 0.1% calcium, upto 4% copper, up to 8% chromium, and the balance essentially iron.

2. An alloy according to claim 1 in which molybdenum is partiallyreplaced on an equal atomic basis by up to 10% tungsten, the molybdenumbeing at least about 10%.

3. An alloy according to claim 1 in which the sum of the columbium,tantalum, boron, zirconium, vanadium, beryllium, calcium, copper andchromium does not exceed 10%.

4. An alloy according to claim 1 and containing up to 1% titanium, up to1% aluminum, the sum of the titanium and aluminum not exceeding 1%, upto 1% columbium, up to 2% tantalum, up to 0.01% boron, up to 0.1%zirconium, up to 1% vanadium, up to 0.1% beryllium, up to 0.05% calcium,up to 1% copper, up to 4% chromium, with the sum of columbium, tantalum,boron, zirconium, vanadium, beryllium, calcium, copper and chromium notexceeding 7%.

5. An alloy according to claim 4 and containing up to 0.5% titanium, andup to 0.5 aluminum.

6. An alloy according to claim 5 and containing up to 0.03% carbon, atleast one element from the group consisting of titanium in an amount of0.1% to 0.5 and aluminum in an amount of 0.1% to 0.5%, up to 0.5%manganese, up to 0.5% silicon, and the balance essentially iron.

7. An alloy according to claim 1 and consisting essentially of about 18%to cobalt, about 14% to 18% molybdenum, about 1% to 4% nickel, tungstenup to 4%, about 0.1% to 0.5% titanium, about 0.1% to 0.5% aluminum, upto 0.25% manganese, up to 0.25% silicon, and the balance essentiallyiron.

8. An alloy characterized by a hardness of about R or higher when agedwithin the temperature range of 850 F. to 1000 F., said alloy consistingessentially of from 15% to 40% cobalt, from 12% to 18% molybdenum, themolybdenum and cobalt being correlated to represent a point within thearea LBEJ KL of the accompanying drawing, 2% to 5% nickel, up to 2%carbon, up to 1.5% titanium, up to 1.5 aluminum, the sum of the titaniumplus aluminum not exceeding about 1.5 up to 0.5% manganese, up to 0.5silicon, up to 10% tungsten, up to 2% columbium, up to 4% tantalum, upto 0.1% boron, up to 0.25 zirconium, up to 2% vanadium, up to 1%beryllium, up to 0.1% calcium, up to 4% copper, up to 8% chromium, andthe balance essentially iron,

References Cited UNITED STATES PATENTS 1,998,953 4/1965 Emmons -126 H2,147,122 2/1939 Emmons 75-126 C 2,801,916 8/1957 Harris 75-128 B2,983,601 8/1961 Fletcher 75-126 C 3,012,879 12/1961 Schempp 75-126 H3,396,013 8/1968 Mihalisin 75-123 HYLAND BIZOT, Primary Examiner U.S.Cl. X.R.

70. THE PRESENCE OF OTHER CONSTITUENTS IN CONTROLLED AMOUNTS, NOTABLYTITANIUM AND/OR ALUMINUM, IS BENEFICIAL.